Septal perforation is a possible complication of septal surgery. Commonly such patients complaints of dryness of nose and occasional whistling sound (very small perforation).
Various factors play a role in formation of these perforation. Most important is handling of flaps on both sides of cartilage. Ideally one septal flap should be lifted intact. (But that is no guarantee that septal perforation will not happen). next even if accidental tears happen on both side of nasal septum then they ideally should not be at same location. Even if that happens then make it sure that a good piece of septal cartilage or bone lies in between the tear.
Try to give quilting suture to hold both flaps in contact so that no dead space forms and do a soft packing so that by pressure blood supply of flap is not hampered with.
Give good broadspectrum antibiotic cover and keep both flaps lubricated or moist with saline spray.